libxml2-legacy is currently in the Testing & Unstable repos:
mbn info libxml2-legacy -q | grep -Ev 'Name|Repository|Packager'
Branch : archlinux
Version : 2.13.8-1
Build Date : Fri 02 May 2025 11:42:34
Branch : unstable
Version : 2.13.8-1
Build Date : Fri 02 May 2025 11:42:34
Branch : testing
Version : 2.13.8-1
Build Date : Fri 02 May 2025 11:42:34
mbn can be found in the manjaro-check-repos package
If you need it urgently, it is not difficult to switch branches:
sudo pacman-mirrors --api --set-branch testing
then
sudo pacman-mirrors --continent && sudo pacman -Syu